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Seeking help with feedback through audio system

I currently use a high mass, direct coupled turntable and have been experiencing some strange "feedback" type issues - I will explain below.

I'd like to know if anyone else has experienced these type of problems and if there is a potential solution.

Situation:
My table sits on a wall shelf (massive & "home made") which connects/integrates with a load bearing wall. I have it set up this way because I have VERY springy hardwood floors which just don't work with any turntable (suspended or non-suspended).

Everything sounds great but at a certain volume level, I begin to hear what I presume to be feedback. It is a steady upper mid-range resonant tone which does not amplify or get louder, it just remains constant until a few seconds after the overall system volume is lowered. The feedback will continue between songs on a record but eventually gets drowned out by the next song and becomes less audible. I can faintly hear the feedback "within" the next song.

When the volume is lowered, the sound is great - with no feedback issues.

I presume this feedback is caused by the interaction between my room and the cartridge (Shelter 901) - which from what I've read may not be a good match for my unipivot tonearm - further complicating or enhancing the problem. I dunno. I did try moving the table to a different location within the room and the same problem occurred when the system was playing at about the same volume - however I think the frequency or tone-of-the-feedback-tone was a bit lower - perhaps mid-bass feedback.

Again, I'd like to know if any of you have experience anything like this and hopefully you've got suggestions on how to alleviate the problem.
bwhite
dougdeacon
3,338 posts
 
It is really weird. There are some facts that I haven't been able to square with each other:

- it starts/stops with moving the stylus on/off the record
- but it's independent of groove modulation
- it starts/stops with the level of the gain control
- but volume doesn't change with changes in gain control

Armtube resonance? Loose cartridge clip vibrating? Phono stage tube resonating? There are objections to all of them.
bornin50
32 posts
 
Hi again

This should be available on a webcast so we could all hear it and chime in with recommendations.

If your electronics have any tone controls or filters, do they have any effect when the 'sound' is active?

I'm getting a 'subsonic stylus in the groove noise aggravating something in the electronics' type of feeling.

Or maybe I'm just on the wrong medication. :-)
viridian's avatar
viridian
4,184 posts
 
There is a very simple test to determine if it is acoustic feedback. With the turntable off, as in not rotating, lower the stylus into a record groove with the volume off. Advance the volume slowly, gently tap the surface that the table is resting on. If feedback is present, you will begin to hear a howling sound at some loudness level. What is happening is that the speakers are amplifing the howl which is picked up by the turntable plinth and amplified, once again, by the cartridge which is.....well, you get it. Warning, keep your hand on the volume control at all times, you will need to rapidly diminish the volume once the volume begins to feed back. Please report if this is the problem. It is generally curable and many times is actually related to the table being cited in a room mode, but we're not there yet.
jea48
2,944 posts
 
How loud is the music you are listening to? Above 90db.If you are cranking the volume up and the music is bouncing off the walls your cartridge will work like a microphone,feedback.You say your TT is fasten to the wall.For a test, take the TT off the wall self and set on a stand.The TT should be behind the front of your speakers to minimize feedback.
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